Gas Compression Process

ABSTRACT

Example embodiments for a method for compressing gas into a liquified gas using a plurality of pairs of liquid gas displacers in parallel moving a working fluid between each pair of displacers to pressurize the gas, arranging sets of the parallel liquid gas displacers in a series to raise the pressure, directly cooling the gas at each displacer pair, and finally condensing the gas using a coolant, collecting the liquified gas, and pressurizing the liquified gas for use in a pipeline.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No. 63/061,049, filed Aug. 4, 2020 and U.S. Provisional Application No. 63/061,059, filed Aug. 4, 2020.

BACKGROUND OF THE INVENTION

To summarize the technology historically utilized in gas compression processes involving low first stage suction pressures would be using a reciprocating or centrifugal compressor to increase the pressure in stages. The pressure increase per stage is limited by the heat of compression temperature increase with material of construction limits of around 225 F. Scrubber vessels are located prior to the inlet of each stage to prevent liquids from entering the compressor. Incompressible liquids can be very harmful to mechanical compressors. The heat of compression is removed from the gas after each stage of compression, usually by an air-cooled exchanger. Some condensation of liquids is common during the cooling of the vapor, so a two-phase separator is located after the cooler to separate condensed liquids. The compression of carbon dioxide, CO₂, to pipeline pressures elevates the gas above critical pressure, where the fluid is compressed/pumped to final pressure.

SUMMARY OF EXAMPLE EMBODIMENTS

An example embodiment may include a method for compressing gas comprising compressing a gas at a first stage compressor to create a first compressed gas, cooling the first compressed gas, compressing the first compressed gas at a second stage compressor to create a second compressed gas, cooling the second compressed gas, compressing the second compressed gas at a third stage compressor to create a third compressed gas, cooling the third compressed gas, compressing the third compressed gas at a fourth stage compressor to create a fourth compressed gas, cooling the fourth compressed gas, condensing the fourth compressed gas into a liquified gas, collecting the liquified gas, pressuring the liquified gas, delivering the liquified gas into a gas line.

A variation of the example embodiment may include the gas being CO₂. The first stage compressor may be a plurality of pairs of displacement vessels each pair having a dedicated pump. The second stage compressor may be a plurality of pairs of displacement vessels each pair having a dedicated pump. The third stage compressor may be a plurality of pairs of displacement vessels each pair having a dedicated pump. The fourth stage compressor may be a plurality of pairs of displacement vessels each pair having a dedicated pump. The first stage compressor may include a plurality of centrifugal pumps. The cooling of the first gas may include using a plurality of discharge coolers. The cooling of the second gas may include using a plurality of discharge coolers. The cooling of the third gas may include using a plurality of discharge coolers. The cooling of the fourth gas may include using a plurality of discharge coolers. The condensing of the fourth gas may include using a plurality of chillers to chill water that is circulated with the gas to condense it. The compressing of the liquified gas may include using a plurality of pumps to increase the pressure.

An example embodiment may include a method for liquifying carbon dioxide comprising receiving carbon dioxide gas from a source, compressing the carbon dioxide in a plurality of pairs of displacer vessels placed in a parallel configuration to form a stage, cooling the gas using a plurality of discharge coolers, one for each pair of displacer vessels, compressing the carbon dioxide using a series of stages in a linear configuration, wherein the pressure of the carbon dioxide is increased and cooled with each stage until the carbon dioxide becomes a liquid, and pumping the liquid carbon dioxide to a pipeline.

An example variation may include the pumps for each of the plurality of pairs of displacer vessels being a centrifugal pump. The pumps for each of the plurality of pairs of displacer vessels may be a vertical wet pit mixed pump. Cooling the gas may include using a plurality of chillers to chill a coolant fluid and then circulating the coolant fluid with the gas. Condensing the gas to liquified gas may include using chilled water in a plurality of displacers. Pressurizing the liquified gas may include using a plurality of pumps.

An example embodiment may include a method for gas comprising receiving gas from a source, compressing the gas a plurality of pairs of displacer vessels placed in a parallel configuration to form a stage, wherein a working fluid is pumped alternatively into the pairs of displacer vessels to pressurize the gas, cooling the gas using a plurality of discharge coolers, one for each pair of displacer vessels, compressing the gas using a series of stages in a linear configuration, wherein the pressure of the carbon dioxide is increased and cooled with each stage until the carbon dioxide becomes a liquid, chilling a coolant and then circulating that coolant within a final stage to produce liquified gas, collecting the liquified gas, pressurizing the liquified gas using a plurality of pumps, and pumping the liquid carbon dioxide to a pipeline.

An example embodiment may include an apparatus for compressing the nearly pure CO₂ byproduct stream from ethanol production facilities. Instead of using a mechanical compressor to compress the gas to 2,200 psig pipeline pressures, the near 0 psig CO₂ would be drawn into a liquid filled vessel by pumping the liquid from the vessel to an adjacent vessel. Once the vessel is emptied of liquid and filled with CO₂, valving would reverse the flow of the liquid and would begin refilling the vessel with liquid. Either check valves or actuated valves would prevent the CO₂ gas from backflowing into the inlet piping. Instead, the gas volume would increase with the rising liquid level resulting in an increase in pressure inside the vessel. Flow of the compressed gas would be routed to a higher-pressure discharge header by the rising liquid displacing the liquid from the vessel into the discharge header. Once the liquid filling sequence is completed, the cycle would begin again with the emptying of the liquid from the vessel, and the drawing in of more low-pressure CO₂. For efficiency, the adjacent vessel that liquid is pumped into and out of is also used to draw in CO₂, compress and displace the compressed vapor into the discharge header. The two vessels working together draw a continuous stream of low-pressure gas in for compression and displacement. Air cooled exchangers will cool the compressed gas after each stage to optimize compression by increasing the density of the gas. Although, the gas is partially cooled by heating the displacement liquid. A heat exchanger on the pump discharge cools the displacement liquid. Once the CO₂ is compressed above 550 psig it can be condensed to a liquid. A multi-stage centrifugal pump or progressive pump is used to pump the liquid CO₂ to the required pipeline pressure of 2,200 psig. Refrigeration can be used to condense the CO₂ at lower pressures, or the gas can be increased to a point where air cooled exchangers can be used to condense the gas. Operating conditions and atmospheric temperatures determine the most economical operation.

An example embodiment may include a method for recompressing the CO₂ used in enhanced oil recovery (EOR). Oil fields using EOR are most productive with low operating pressure recompression headers operating less than 50 psig. Recompressed CO₂ is returned to the oilfield and reinjected at pressures above 2,000 psig. Instead of using a mechanical compressor to compress the gas to 2,200 psig pipeline pressures, the near less than 100 psig CO₂ would be drawn into a liquid filled vessel by pumping the liquid from the vessel to an adjacent vessel. Once the vessel is emptied of liquid and filled with CO₂, valving would reverse the flow of the liquid and would begin refilling the vessel with liquid. Either check valves or actuated valves would prevent the CO₂ gas from backflowing into the inlet piping. Instead, the gas volume would increase with the rising liquid level resulting in an increase in pressure inside the vessel. Flow of the compressed gas would be routed to a higher-pressure discharge header by the rising liquid displacing the liquid from the vessel into the discharge header. Once the liquid filling sequence is completed, the cycle would begin again with the emptying of the liquid from the vessel, and the drawing in of more low-pressure CO₂. For efficiency, the adjacent vessel that liquid is pumped into and out of is also used to draw in CO₂, compress and displace the compressed vapor into the discharge header. The two vessels working together draw a continuous stream of low-pressure gas in for compression and displacement. The gas is usually 85-95% CO₂. The balance of the composition is the full spectrum of volatile hydrocarbons found in oilfield gas. Air cooled exchangers will cool the compressed gas after each stage to optimize compression by increasing the density of the gas. Some hydrocarbons will be condensed as the gas pressure increases and are removed in a separator downstream of the coolers. Although, the gas is partially cooled by heating the displacement liquid. A heat exchanger on the pump discharge cools the displacement liquid. Once the CO₂ is compressed above 550 psig it can be condensed to a liquid. Some non-condensables will pass through the condenser and can be vented to a fuel-gas header or an alternative purpose in the processing facility. A multi-stage centrifugal pump or progressive pump is used to pump the liquid CO₂ to the required pipeline pressure of 2,200 psig. Refrigeration can be used to condense the CO₂ at lower pressures, or the gas can be increased to a point where air cooled exchangers can be used to condense the gas. Operating conditions and atmospheric temperatures determine the most economical operation.

BRIEF DESCRIPTION OF THE DRAWINGS

For a thorough understanding of the present invention, reference is made to the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings in which reference numbers designate like or similar elements throughout the several figures of the drawing. Briefly:

FIG. 1 depicts an example embodiment of a flow diagram of a liquid-piston CO₂ compression process, first stage.

FIG. 2 depicts an example embodiment of a flow diagram of a liquid-piston CO₂ compression process, second stage.

FIG. 3 depicts an example embodiment of a flow diagram of a liquid-piston CO₂ compression process, third stage.

FIG. 4 depicts an example embodiment of a flow diagram of a liquid-piston CO₂ compression process, fourth stage.

FIG. 5 depicts an example embodiment of a flow diagram of a liquid-piston CO₂ compression process, condensation and final pressure pumping.

FIG. 6 depicts an example embodiment of a flow diagram of a liquid-piston CO₂ compression process, process flow diagram with material balance.

DETAILED DESCRIPTION OF EXAMPLES OF THE INVENTION

In the following description, certain terms have been used for brevity, clarity, and examples. No unnecessary limitations are to be implied therefrom and such terms are used for descriptive purposes only and are intended to be broadly construed. The different apparatus, systems and method steps described herein may be used alone or in combination with other apparatus, systems and method steps. It is to be expected that various equivalents, alternatives, and modifications are possible within the scope of the appended claims.

The general process flow takes low pressure CO₂ gas from the low-pressure source through the various equipment in the compression technology. The fluid is compressed, and the heat of compression removed to increase compression efficiency. The fluid is condensed at high pressure and pumped to a pipeline for transport.

The example embodiments fit an anthropogenic CO₂ source and will have a standard set of design elements, described herein is designed to accommodate a range of operating conditions to optimize the compression of CO₂ produced to pipeline transport pressures. The CO₂ can then be used in the energy or manufacturing industries. Anthropogenic CO₂ is produced from many different processes such as Transportation, Electricity Production, Industrial Processes, Commercial and Residential Heating, and Agriculture. The process is more economical on larger scales, as such is most suitable for Electricity Production and Industrial Processes such as ethanol production facilities.

An example embodiment is disclosed in FIG. 1 as the first stage of the liquid piston CO₂ compression process 500. CO₂ flow 502 enters one of the displacer vessels, 503(a-e), 504(a-e) where liquid from one of the pumps 505(a-e) moves liquid into the displacer, displacing the CO₂ out of the displacer and to one of the gas coolers 501(a-e). Cooled gas leaves the gas coolers 501(a-e) and proceeds to the second stage through header 506. Pumps 505(a-e) are shown as vertical pumps, but they can be any type of pump, including centrifugal pumps. The displacer vessels 503(a-e) rely on a working fluid to compress the gas, in this case CO₂. Any pump that can pump a working fluid, such as water in this example embodiment, can be used as a pump 505(a-e). Working fluids could include water, water glycol mix, hydraulic fluid, produced oil, hydrocarbon by-product, produced water, or any other suitable working fluid.

The displacer vessels 503(a-e) and 504(a-e) may be displacement tanks that can be either horizontal or vertical in orientation. The displacer vessels 503(a-e) and 504(a-e) are sized based on the frequency of valve cycling desired. Displacer vessels 503(a-e) and 504(a-e) sized to fill in approximately 30 seconds would experience about one million valve cycles per year. Valves and actuators with two million cycle life estimates would provide two years of operation without anticipated valve maintenance.

The liquid displacer pumps 505(a-e) are centrifugal. The pumps 505(a-e) will operate along their design operating curve between the beginning and ending pressure of the displacer vessels 503(a-e) and 504(a-e). For the rated gas flow rate of the unit, the pumps 505(a-e) must displace the corresponding volume of liquid to match the actual volume of the gas flowed during the compression cycle. The density of the gas progressively increases during the compression step as the displacer pressure increases.

The pumping or compressing cycle of the liquid piston unit is controlled with low liquid level switches on each volume displacer tank. The on-off valves are piped so that the pump discharge can be routed to either tank. Likewise, the pump suction can be lined up with either tank. When the liquid level switch of the tank being emptied activates, the valves switch so that the tank that was being emptied now becomes the tank being filled.

Inlet gas is routed to the top of each of the displacer vessels 503(a-e) and 504(a-e). A check valve at the inlet of each displacer vessels 503(a-e) and 504(a-e) only allows gas to enter but not exit. The dropping liquid in the displacer vessels 503(a-e) and 504(a-e) being emptied draws gas into the tank. The rising liquid level in the displacer vessels 503(a-e) and 504(a-e) being filled displaces gas from each of the displacer vessels 503(a-e) and 504(a-e), but the check valve on the inlet header prevents back-flow of the gas. Instead the gas exits into the discharge header. The discharge header also has check valves where the header attaches to each pair of displacer vessels 503(a-e) and 504(a-e). However, the check valves only allow gas to exit the displacer vessels 503(a-e) and 504(a-e) and flow into the discharge header. If too much gas is drawn through the displacer vessels 503(a-e) and 504(a-e), the suction pressure will drop below the desired pressure set point. To control the suction pressure, a valve allows some gas from the discharge header to flow back to the inlet header.

Higher differential pressures can be achieved if displacer vessels 503(a-e) and 504(a-e) are linked in series. Multiple stages of compression are more efficient than one large pressure differential stage. As the gas compresses, less and less volume of liquid is required to displace the same SCFM flow rate of gas. The denser gas that requires less liquid displacement requires less pumping horsepower. Interstage pressures are maintained and balanced with feathering control valves on the gas header from the discharge of a stage back to its suction. Heat of compression is removed with an appropriately sized heat exchanger(s), in this example gas coolers 501(a-e).

An example embodiment is disclosed in FIG. 2 as the second stage of the liquid piston CO₂ compression process 510. CO₂ flow 506 enters one of the displacer vessels, 513(a-e), 514(a-e) where liquid from one of the pumps 515(a-e) pumps liquid into the displacer, displacing the CO₂ out of the displacer and to one of the gas coolers, 511(a-e). Cooled gas leaves the cooler and proceeds to the second stage through header 516.

An example embodiment is disclosed in FIG. 3 as the third stage of the liquid piston CO₂ compression process 520. CO₂ flow 516 enters one of the displacer vessels, 523(a-e), 524(a-e) where liquid from one of the pumps 525(a-e) pumps liquid into the displacer, displacing the CO₂ out of the displacer and to one of the gas coolers, 521(a-e). Cooled gas leaves the cooler and proceeds to the second stage through header 526.

An example embodiment is disclosed in FIG. 4 as the fourth stage of the liquid piston CO₂ compression process 530. CO₂ flow 526 enters one of the displacer vessels, 533(a-e), 534(a-e) where liquid from one of the pumps 535(a-e) pumps liquid into the displacer, displacing the CO₂ out of the displacer and to one of the gas coolers, 531(a-e). Cooled gas leaves the cooler and proceeds to the second stage through header 536.

An example embodiment is disclosed in FIG. 5 as the fourth stage of the liquid piston CO₂ compression process 540. CO₂ flow 536 enters one of the vapor condensers, 542(a-e), where CO₂ is condensed and collected in one of the liquid receivers, 543(a-e). Vapor condensers 542(a-e) is a heat exchanger. Vapor entering via CO₂ flow 536 is cooled by vapor condensers 542(a-e), utilizing cooled water recirculating via pumps 545(a-h) from chillers 541(a-h). As the vapor cools it condenses into liquid, that liquefied gas is then collected first in liquid receiver tanks 543(a-e), then pumps, such as multi-stage centrifugal pump, 544(a-e), raises the pressure of the liquid gas and feeds it into the pipeline. Cooling for the 542(a-e) condensers is provided by recirculating the chilled liquid through chillers 541(a-h) using chilled water pumps 545(a-h). Liquid CO₂ from 5th stage liquid receiver, 543(a-e) is pumped to pipeline pressure using 5^(th) stage liquid CO₂ pumps, 544(a-e). High-pressure liquid CO₂ leaves the process through header 546. The chilled liquid is a coolant and can be water or some other suitable coolant liquid. The coolant may be circulated within the vapor condensers 542(a-e) using piping or coils to maximize heat transfer between the coolant and the gas being condensed.

Pumps 505(a-e) are different from other pumps, such as 515(a-e) for economic reasons. At the high flow rates required for the first stage, the cost of traditional horizontal pumps is significantly higher than that of vertical wet pit mixed flow pumps. These vertical wet pit mixed flow pumps are normally used in agriculture and in industrial cooling towers where relatively low head and very high flows are required.

The chillers used in stage 5 are different than the air coolers in stages 1-4 because of pressures and temperatures involved. With CO₂ there are two potential paths to take in converting the gas to a liquid. One path is to use only compression, taking the gas above the critical point and compressing it to a point that when cooled back to atmospheric temperatures it becomes a liquid out of the critical region. The second path is more economical wherein the gas is compressed only up to a point so that when a chiller is employed the gas condenses. This requires less horsepower to pump the liquid up to pipeline pressure of about 2,200 psig. Depending on the refrigeration temperatures used, the compression point can be as low as 250 psig, or up to about 700 psig. Relatively mild refrigeration using off-the shelf chillers may be more practical and less expensive in the example embodiments.

The vapor condensers in stage 5 are necessary because the stage 5 is the breakover point where compression stops and condensing starts so that multi-stage centrifugal pumps can bring the pressure from 700 psig to 2,200 psig.

FIG. 6 shows an example embodiment of the stages 1-5 linked together. First stage of the liquid piston CO₂ compression process 500 takes energy Q-1 to compress CO₂ which is then cooled in first stage discharge coolers 501(a-e) where energy Q-6 is removed resulting in the compressed CO₂ output 506. The output 506 of the first stage is then fed into the second stage compression process 510 using energy Q-2 to compress the CO₂, which is then cooled in the second stage discharge coolers 511(a-e) where energy Q-7 is removed, resulting in compressed CO₂ output 516. The output 516 of the second stage is then fed into the third stage compression process 520 using energy Q-3 to compress the CO₂, which is then cooled in the third stage discharge coolers 521(a-e) where energy Q-8 is removed, resulting in compressed CO₂ output 526. The output 526 of the third stage is then fed into the fourth stage compression process 530 using energy Q-4 to compress the CO₂, which is then cooled in the fourth stage discharge coolers 531(a-e) where energy Q9 is removed, resulting in compressed CO₂ output 536. Compressed CO₂ 536 is then fed into the fifth stage pump 540 where energy Q-5 is used to condense the CO₂ into a liquid, collect the liquified portion, and then pressurize it up to the line pressure, typically around 2,200 psig, and then produce an output 546 of pressurized liquified CO₂.

The displacer vessels can use a working fluid to compress the gas, in this case CO₂. The working fluid can be in direct contact with the gas, it can be contained in a bladder that expands, or there could be a physical piston within the displacer vessel separating the gas from the working fluid. Any pump that can pump a working fluid, such as water in the disclosed example embodiments. Suitable working fluids include water, water glycol mix, hydraulic fluid, produced oil, hydrocarbon by-product, produced water, or any other suitable working fluid.

The gas being compressed to a liquid in the disclosed examples is CO₂. However, any gas or vapors could be compressed using the disclosed embodiments, with modifications to account for different pressures, temperatures, and other properties associated with phase changes for a particular gas.

The displacer vessels may be displacement tanks that can be either horizontal or vertical in orientation. The displacer vessels are sized based on the frequency of valve cycling desired.

The liquid displacer pumps may be centrifugal, vertical, positive displacement, or any other pumps suitable for the desired working fluid at the desired temperature and pressure. The pumps will operate along their design operating curve between the beginning and ending pressure of the displacer vessels. For the rated gas flow rate of the unit, the pumps must displace the corresponding volume of liquid to match the actual volume of the gas flowed during the compression cycle. The density of the gas progressively increases during the compression step as the displacer pressure increases.

The example embodiments will be equipped with multiple PLCs and/or a DCS control system. The controls and will be powered via UPS power. Electric valves, if installed, considered to be critical for a safe shutdown of the process will be powered by the battery backup boxes. UPS supply will be from a 24 VDC Battery Box or a redundant power supply. In case of absence of Main Utility power, the batteries at the battery-backup boxes will provide enough backup time to the process DC S/PLC, critical valves, and critical instrumentation throughout the process with the purpose of a safely shutdown of the process and have the ability to identify and monitoring the main process variables and parameters during this time. 

What is claimed is:
 1. A method for compressing gas comprising: compressing a gas at a first stage compressor to create a first compressed gas; cooling the first compressed gas; compressing the first compressed gas at a second stage compressor to create a second compressed gas; cooling the second compressed gas; compressing the second compressed gas at a third stage compressor to create a third compressed gas; cooling the third compressed gas; compressing the third compressed gas at a fourth stage compressor to create a fourth compressed gas; cooling the fourth compressed gas; condensing the fourth compressed gas into a liquified gas; collecting the liquified gas; pressuring the liquified gas; delivering the liquified gas into a gas line.
 2. The method for compressing gas of claim 1 wherein the gas is CO₂.
 3. The method for compressing gas of claim 1 wherein the first stage compressor is a plurality of pairs of displacement vessels each pair having a dedicated pump.
 4. The method for compressing gas of claim 1 wherein the second stage compressor is a plurality of pairs of displacement vessels each pair having a dedicated pump.
 5. The method for compressing gas of claim 1 wherein the third stage compressor is a plurality of pairs of displacement vessels each pair having a dedicated pump.
 6. The method for compressing gas of claim 1 wherein the fourth stage compressor is a plurality of pairs of displacement vessels each pair having a dedicated pump.
 7. The method for compressing gas of claim 1 wherein the first stage compressor includes a plurality of centrifugal pumps.
 8. The method for compressing gas of claim 1 wherein the cooling of the first gas includes using a plurality of discharge coolers.
 9. The method for compressing gas of claim 1 wherein the cooling of the second gas includes using a plurality of discharge coolers.
 10. The method for compressing gas of claim 1 wherein the cooling of the third gas includes using a plurality of discharge coolers.
 11. The method for compressing gas of claim 1 wherein the cooling of the fourth gas includes using a plurality of discharge coolers.
 12. The method for compressing gas of claim 1 wherein the condensing of the fourth gas includes using a plurality of chillers to chill water that is circulated with the gas to condense it.
 13. The method for compressing gas of claim 1 wherein the compressing of the liquified gas includes using a plurality of pumps to increase the pressure.
 14. A method for liquifying carbon dioxide comprising: Receiving carbon dioxide gas from a source; Compressing the carbon dioxide in a plurality of pairs of displacer vessels placed in a parallel configuration to form a stage; Cooling the gas using a plurality of discharge coolers, one for each pair of displacer vessels; Compressing the carbon dioxide using a series of stages in a linear configuration, wherein the pressure of the carbon dioxide is increased and cooled with each stage until the carbon dioxide becomes a liquid; and Pumping the liquid carbon dioxide to a pipeline.
 15. The method for liquifying carbon dioxide of claim 14 wherein the pumps for each of the plurality of pairs of displacer vessels is a centrifugal pump.
 16. The method for liquifying carbon dioxide of claim 14 wherein the pumps for each of the plurality of pairs of displacer vessels is a vertical wet pit mixed pump.
 17. The method for liquifying carbon dioxide of claim 14 further comprising cooling the gas using a plurality of chillers to chill a coolant fluid and then circulating the coolant fluid with the gas.
 18. The method for liquifying carbon dioxide of claim 14 further comprising condensing the gas to liquified gas using chilled water in a plurality of displacers.
 19. The method for liquifying carbon dioxide of claim 18 further comprising pressurizing the liquified gas using a plurality of pumps.
 20. A method for gas comprising: receiving gas from a source; compressing the gas a plurality of pairs of displacer vessels placed in a parallel configuration to form a stage, wherein a working fluid is pumped alternatively into the pairs of displacer vessels to pressurize the gas; cooling the gas using a plurality of discharge coolers, one for each pair of displacer vessels; compressing the gas using a series of stages in a linear configuration, wherein the pressure of the carbon dioxide is increased and cooled with each stage until the carbon dioxide becomes a liquid; chilling a coolant and then circulating that coolant within a final stage to produce liquified gas; collecting the liquified gas; pressurizing the liquified gas using a plurality of pumps; and pumping the liquid carbon dioxide to a pipeline. 